Introduction: Rumination is characterized by frequent effortless regurgitation of recently ingested food, followed by expulsion or re-swallowing. Rumination syndrome may be misdiagnosed as refractory gastroesophageal reflux disorder leading to Nissen fundoplication; the outcome in rumination syndrome is unclear. Aims: To evaluate the outcomes of Nissen fundoplication in the treatment of rumination syndrome and describe outcomes of behavioral therapy after Nissen fundoplication. Methods: We conducted a cross-sectional study by reviewing medical records of patients diagnosed with rumination syndrome from 1995 to 2015 who had undergone Nissen fundoplication elsewhere, prior to the diagnosis at Mayo Clinic. Twelve patients, aged 23-65y, were invited to participate in a questionnaire survey. The variables studied included age, sex, race, duration of symptoms, associated symptoms, initial upper GI symptoms, upper GI symptoms after Nissen fundoplication, investigations, and management. Results: Among the 12 patients, 10 were female, age at diagnosis was 32.3+13.8y (SD), and duration of symptoms before diagnosis was 9.8+9.9y. Seven patients (58.3%) were receiving psychiatric medications. Initial symptoms were: regurgitation (4/12), acid reflux (3/12), both regurgitation and acid reflux (2/12), vomiting in 3/12. Symptoms recurred within 3 months of the Nissen fundoplication in 7/12, and within 1.5-6 years in 3/12 patients. Two patients reported 40% and 70% improvement in their symptoms after Nissen fundoplication; in contrast, severity of upper GI symptoms increased in 9/12 patients. Before the diagnosis of rumination syndrome, Nissen procedure was redone in 2/12, revised in 3/12, and taken down in 3/12. Three of the 12 patients required tube feeding (1 each nasogastric, gastric, jejunal) after Nissen fundoplication, and 4/12 required multiple esophageal dilatations. After the diagnosis of rumination syndrome, all patients underwent behavioral therapy and were taught to perform diaphragmatic breathing during and after meal ingestion. Eight patients consented to participate in a follow-up questionnaire at least 6 months after this therapy; behavioral therapy helped control regurgitation symptoms >80% of the times in 4/8, 60-80% of the times in 1/8, and < 20% in 3/8 patients. Conclusion: Behavioral therapy with diaphragmatic breathing may be efficacious in controlling regurgitation associated with rumination syndrome after Nissen fundoplication.